1. Field
This relates generally to the manufacturing of semiconductor devices and, more specifically, to forming punch-through stopper regions for fin field effect transistor devices.
2. Related Art
As semiconductor manufacturers continue to shrink the dimensions of transistor devices in order to achieve greater circuit density and higher performance, short-channel effects, such as parasitic capacitance and off-state leakage, increasingly impair transistor device characteristics. Fin field effect transistors (finFETs), such as double-gate transistors, tri-gate transistors, and gate-all-around transistors, are a recent development in semiconductor processing for controlling such short-channel effects. A finFET has a fin that protrudes above a substrate surface. The fin forms the body of the finFET device and has fewer paths for current leakage than a planar body. Additionally, the fin creates a longer effective channel width, thereby increasing the on-state current and reducing short channel effects.
FinFET devices may be formed on bulk semiconductor substrates. One issue of forming finFET devices on bulk semiconductor substrates may be the existence of a leakage path at the bottom of the fin where gate control terminates. This leakage path may cause significant sub-threshold punch-through leakage (e.g., short channel leakage effect) and may prohibit further scaling of the channel length. To substantially reduce punch-through leakage, a punch-through stopper region may be formed at the base of the fin using an ion implant process. One conventional method of forming a punch-through stopper region may be to implant a high concentration of dopant ions into the substrate prior to forming the fin. In particular, the dopant ions may be implanted at a target depth that coincides with the base of the subsequently formed fin. However, due to the implant depth profile following an approximate Gaussian distribution, there may be a concentration gradient of dopant ions implanted between the surface of the substrate and the target depth. This may result in a non-uniform dopant profile across the active channel region of the subsequently formed fin, which may cause undesirable variations in the threshold voltage across the height of the resultant fin channel.